I sent out a reply earlier today, but it never showed up. If it does, then I will probably delete this one.
We are just starting the iOS development and since I am not the primary developer, I am not sure what versions would be supported. I am sure we are using the current version of the OS to develop on so I think whatever legacy support Apple provides in their development tools would provide some backward compatibility with older versions. As far as the display size goes, we will probably develop a different screen layout with some things removed so that it is useful on the iPhone.
As far as Android is concerned, our ExploreStars app will run on version 4.4 KitKat and newer. Since that was released back in 2013, you should be able to use any tablet at least that old and any older one's that you can upgrade the OS to KitKat.
The recommended tablet size is 7-inches. 8-inches is better, and 10-inches is a luxury. I would consider a Windows or Android 7, and 8-inch tablet only good to run ExploreStars only. If you want just one tablet that you can use as a remote access computer and also locally with a gamepad controller, then I would get a Windows 10-inch tablet that runs Windows 10.
This will allow you to have the equivalent of a single-board computer (SBC) that people are starting to use, along with a local display when you are at the mount. You can run the ASOM clients of your choice on it and also ASCOMPAD gamepad interface and TeamViewer for remote access.
Director Electrical Engineering
Explore Scientific, LLC.